1. Field of the Invention
This invention relates to a semiconductor layer containing, as a principal constituent, a Groups III-V semiconductor compound, which may be represented by the general formula BxAlyGazN, wherein x represents a number satisfying the condition 0<x<1, y represents a number satisfying the condition 0≦y<1, and z represents a number satisfying the condition 0<z<1, with the proviso that x+y+z=1. This invention also relates to a process for forming the semiconductor layer. This invention further relates to a semiconductor light emitting device, which comprises the semiconductor layer.
2. Description of the Related Art
In recent years, GaN type materials have been developed, and rapid advances have been made in semiconductor light emitting devices, such as semiconductor lasers and light emitting diodes, which are capable of producing light having short wavelengths. Nowadays, semiconductor light emitting devices, which are capable of producing light having a wavelength of as short as 365 nm, have been accomplished. Also, nowadays, extensive studies are being conducted on semiconductor light emitting devices, which are capable of producing light having a shorter wavelength.
One of semiconductor light emitting devices, which are greatly expected to be appropriate as ultraviolet semiconductor light emitting devices, is an AlGaN type semiconductor light emitting device, in which a GaN base plate is used as a base plate, and in which a mixed crystal material of GaN with AlN or with AlInN (specifically, an AlGaN mixed crystal or an AlGaInN mixed crystal) is caused to grow on the GaN base plate. For example, it has been reported that, with a device structure of a GaN base plate/AlGaN type quantum well structure, production of a laser beam having a wavelength of approximately 240 nm is capable of being achieved though with light excitation. The report is made in, for example, “Room-temperature deep-ultraviolet lasing at 241.5 nm of AlGaN multiple-quantum-well laser”, T. Takano et al., Applied Physics Letters, Vol. 84, No. 18, pp. 3567-3569, 2004.
However, under existing circumstances, there is no prospect of use of ultraviolet semiconductor light emitting devices, in practice. It is thought that one of causes of the aforesaid problems encountered with the ultraviolet semiconductor light emitting devices is that it is not always possible to accomplish the crystal growth. In cases where the light emitting device is to be produced with the material system described above, in order for the light having a short wavelength to be produced, it is necessary that the Al quantity in the AlGaN mixed crystal or the AlGaInN mixed crystal be set to be large. However, in cases where the Al quantity in the AlGaN mixed crystal or the AlGaInN mixed crystal is set to be large, crystal defects are apt to increase, and it is not always possible to achieve conversion into a p-type. Therefore, limitation is imposed upon the increase in Al quantity in the AlGaN mixed crystal or the AlGaInN mixed crystal.
Also, AlGaN type semiconductor light emitting devices, in which an MnO base plate or an SiC base plate is used as the base plate, have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 1(1989)-017484 and 5(1993)-206513. However, even though the kind of the base plate is altered, in order for the light having a short wavelength to be produced, it is still necessary that the Al quantity in the AlGaN mixed crystal or the AlGaInN mixed crystal be set to be large. Therefore, with the techniques proposed in, for example, Japanese Unexamined Patent Publication Nos. 1(1989)-017484 and 5(1993)-206513, the problems described above are not capable of being solved.